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RMAN took 12hrs to restore

Last week, I had to perform recovery on a unix database using RMAN...
My only concern about this whole recovery is the fact that it took RMAN 12hours to restore the 150gb files from tape. In the previous mock recoveries, the restores has taken about 3 hours maxium. I couldnt figure out why it took to much time.. everything is the same. the data has grown by 15%. The hotbackup takes about 3.5hrs to backup at incremental 0 (full). Can you kindly make some suggestions?

Just to backup (get it!) what Axr2 said, I started adding more channels to my backups to find the optimal setting. Three channels was great but when I added a fourth, performance got worse. We didn't have the bandwidth to support it

I agree with Hacketta1 & Axr2. That's way too many channels. Did it actually use all of them? Do you have that many devices in your tape system? RMAN should only use as many channels as devices available.

Another possibility - was anything else going on on your tape system at the same time? Other systems backing up? Reclimation? System level backups?

Whenever I have to restore, I always make sure my tape system stops all other processes for the duration of the restore.

Originally posted by jlakhani so what you are really saying is that by over allocating more channels, I can actually slow down the rman restore? howz that possible? can somebody explain me that?

They will compete for bandwidth. Can you answer some of my questions? Were all the channels used in the restore? Do you have that many tape devices? Was anything else being done on the tape system at the same time?

You need to benchmark backups with different channels... take the size of the backup file divide by the time it took to back up. Do this for each piece that is backed up (i.e channel). Sum it up for all the pieces. You will get your throughput and you can see what is optimal. You may get 10M a minute with 2 channels, but only get 7M a minute with 3 channels, etc. I'd use the same for restore that I used to back up. How many do you use on your daily backups that take 3 hours?

Also, a restore WILL take longer than a backup... and depending on how many archive logs you have to restore, that will add time too. But it shouldn't be 4x.

Lastly, there could be a problem with your tape system. I have had to do a few restores here, and every once in a while, I will watch how much data is coming across, and I'll get like 30 MEG in 1 hour. It's weird. I stop and start the restore, and it flies. Nobody here knows why, and I know how to fix it, so if I see it I just stop it and start over. So I would watch the restore rate to see if you have some problem there too.

Jodie,
I dont think all the channels were used for the restore. they configured 2 tapes to work with this backup via Omniback 4:data protector. So I used the restore command directly from the Omniback Specs...

Originally posted by jlakhani Jodie,
I dont think all the channels were used for the restore. they configured 2 tapes to work with this backup via Omniback 4:data protector. So I used the restore command directly from the Omniback Specs...

If you have only 2 tape devices - don't bother configuring more than 2 channels. Adding more only helps if your restoring from disk. I'd still check to see if anything else was running at the same time.